Limb lengthening surgery is an option for individuals who have discrepancies in limb length. Certain health conditions can lead to unequal limb lengths such as birth defects, previous injuries or broken bones, poliomyelitis, cerebral palsy, hip diseases, and muscular defects. See http://www.nlm.nih.gov/medlineplus/ency/article/002965.htm. Common approaches to limb lengthening surgery include external fixation (alone), fully implantable lengthening nails, and a combination of lengthening over nail with external fixation. See http://www.lifebridgehealth.org/RIAO/TheConcept.aspx.
Limb lengthening using external fixation (such as by using the Ilizarov method uniplanar limb reconstruction system) are well-known techniques that has been used for treatment of many complicated conditions as congenital and post traumatic bone deformity, short stature treatment, bone infection and nonunion, after removal of tumors to reconstruct or lengthen the bone and soft tissues. In addition to being used to support a fractured limb, the Ilizarov frame is also commonly used to correct deformity through distraction osteogenesis (also known as distraction callotasis and osteodistraction).
In a general distraction osteogenesis procedure, the bone, if not already fractured, is purposely fractured surgically (corticotomy or osteotomy), and the two segments of bone are gradually distracted apart, which allows new bone to form in the gap therebetween. Generally, the rate of gradually distracting the two segments of bone apart is from half to one millimeter per day till the bone reaches the desired length. If the distraction rate is too quick, there is a risk of non-union. If the distraction rate is too slow, there is a risk that the two segments of bone will completely fuse to each other before the distraction period is complete. When the desired length of the bone is achieved using this process, the bone is allowed to consolidate. Distraction osteogenesis applications are mainly focused on the growth of the femur or tibia, but may also include other bones, like the humerus.
Distraction osteogenesis using external fixators has been done for many years. Such a procedure is done by the use of external fixation, which is bulky and with pins attached to the bone and coming out of the skin. Then the fixation need to stay till full consolidation of the new soft bone that was formed and full calcification which usually take about double the duration of lengthening. By way of example, seven centimeters lengthening by the external fixation would generally need to stay for about 7 months or more. Images of distraction osteogenesis using external fixators is depicted in FIGS. 1A-1B.
The external fixator can be unwieldy for the patient. It can also be painful, and the patient is subject to the risk of pin track infections, joint stiffness, loss of appetite, depression, and other side effects. Having the external fixator in place also delays the beginning of rehabilitation.
In response to the shortcomings of external fixator distraction, intramedullary distraction nails have been surgically implanted which are contained entirely within the bone. These are referred to as intramedullary (inside the bone) lengtheners. An image of distraction osteogenesis using an intramedullary distraction nail is depicted in FIG. 1C. In some embodiments, these devices are automatically lengthened via repeated rotation of the patient's limb. This can sometimes be painful to the patient, and can often proceed in an uncontrolled fashion. This therefore makes it difficult to follow the strict daily lengthening regime that avoids non-union (if too quick) or early consolidation (if too slow).
Other intramedullary nails have been developed that have an implanted motor and are remotely controlled. In some instances, the motorized intramedullary nails have an antenna that needs to be implanted subcutaneously, thus complicating the surgical procedure, and making it more invasive. These devices are therefore designed to be lengthened in a controlled manner, but due to their complexity, may not be manufacturable as an affordable product. Others have utilized intramedullary distracters containing an implanted magnet, which allows the distraction to be driven electromagnetically by an external stator (i.e., a large electromagnet). U.S. Pat. No. 8,449,543, “Bone Growth Device And Method,” issued May 28, 2013, to Pool et al. (“Pool '543 Patent”), discloses an intramedullary lengthening device that includes a housing, a distraction shaft, a permanent magnet, and a lead screw. The permanent magnet is configured for rotation relative to the housing with the permanent magnet operatively coupled to a lead screw with a threaded portion that can extend the distraction shaft.
There are a number of criteria that must be present for the use of these nails. This criteria includes: wide bone medulla to put these large nails inside, no bone deformity or curve, and skeletally mature bone as in adults (because the nail will destroy the growth plate in children bone), so these nails cannot be used for bone lengthening in children. Another common problem is the mechanical failure of the nail or nail jamming Also these nails are very expensive.
The concept of extramedullary lengtheners (on the surface of the bone) is also known in the prior art and these can be used for children, as opposed to intramedullary lengtheners. This is because intramedullary lengtheners involve the growth plates in both the femur and the tibia. For example, antegrade cannulization, i.e., inserting a tube into a hollow inside of a bone, of the femur not only disrupts the greater trochanter growth plate, but can also lead to avascular necrosis of the femoral head in children and certainly can disrupt growth quite significantly in the tibia, if the children's growth plates are open. Another issue is that intramedullary channels in children have small diameters that often do not leave sufficient room for intramedullary lengthening devices.
U.S. Patent Appl. Publ. No. 2005/0234448, published Oct. 20, 2005, to McCarthy is a prior art example of an extramedullary lengthener. The McCarthy device features extramedullary elongation devices for lengthening one or more bones, the devices implanted adjacent to the bone and under the skin of a patient using minimally invasive techniques. The device includes a frame having smooth edges and an end with a smooth contour, a first plate attached to the frame and configured to be secured to the bone, the first plate having smooth edges, a second plate configured to be secured to the bone, the second plate having smooth edges, a rod (which may be enclosed by the frame) linked to the first plate, an actuator secured either to the rod or the second plate, and a block secured to the second plate, the block linked to the rod such that actuation of the actuator results in displacement of the second plate relative to the first plate.
The McCarthy device does not require exposed hardware (that can lead to infection) or skin and muscle penetration from the pins (that cause pain), and produce minimal scarring from pin sites because the devices are placed under the skin of a patient using minimally invasive techniques. The McCarthy device can be designed with smooth contours to enable implantation using minimally invasive techniques. The devices can be actuated using an actuator that is externally or internally powered. In the case of external power, the McCarthy device can be powered remotely through high frequency transmission of power through the skin.
Another example of an extramedullary lengthener is disclosed in Pool '543 Patent. The Pool device can alternatively be applied to distractible bone plates that are not located within the intramedullary canal, but are external to the bone.
U.S. Pat. No. 5,902,304, issued May 11, 1999 to Walker et al. is a telescopic bone plate for distracting osteotomically separated bone sections. The telescopic bone plate consists of a top bone plate and a bottom bone plate longitudinally, laterally and vertically adjustable relative to each other and including a device for fastening the telescopic bone plate to bone. The Walker device has a telescopic member that adjusts the relative positions of the top and bottom bone plate to each other. The Walker device telescopic member is actuated internally to the patient and may be actuated intraorally in one variation.
PCT Int'l Pat. Appl. Publ. No. WO2009/062522, “E-Plate (Bone Lengthening Plate), published May 22, 2009, to Emara et al. (the “PCT '522 Application”) discloses a fixator distraction device is also put internally and rests on the surface (rather than inside) the bone and is remotely controlled from the outside. This extramedullary lengthener device was directed to a wide variety of patients including children and those patients having small bone size, who are the most common type of patients that would need limb lengthening. While the PCT '522 Application discloses that a special small motor is to be connected to the telescopic power crew to elongate the device, and that this motor is remotely controlled from the outside this application does not reveal the manner in which the elongation is effectuated and the mechanisms that are to be implemented to controllably elongate the device.